Long-term integrators can be used, for example, for the measurement of a magnetic flux and determining derivative values therefrom. The sensor for this purpose can include a coil whose output or measurement voltage is applied to the long term integrator.
In prior art analog integrators, a series resistance of an operational amplifier is provided at the input side thereof and a condenser forms a parallel network therewith. Such long-term integrators have been found to have drawbacks especially with respect to their drift and poor long term precision. These drawbacks are not readily controllable.
The input steady or quiescent current and the offset voltage of the operational amplifier, for example, cause errors in the final result which are not negligible. The integration constant is dependent upon the capacity of the condenser and the resistance of the series resistor which cannot be selected at will. Error sources also include the leakage current through the condenser and its polarization voltage.
Another kind of integration process utilizes counter methods. In these methods, signals are integrated by summing in accordance with the trapezoidal law. A drawback of such systems is the relatively low numerical precision and slow speed of the integration process
With the advances in microelectronics in recent years and, especially, the development of programmable digital signal processors (DSP) analog processes can be replaced by digital processes.
In the digital signal processing, arithmetic operations, like addition and multiplication are used. Such operations are free from variations and fluctuations of the type which has characterized nondigital integration methods.
It is thus possible to realize signal processing systems with very high precisions using digital techniques. These are applicable to long term integrators as well.
While digital signal processing has significantly reduced tendencies to error, offset voltages which can result from the analog-digital converter and the optionally provided DC voltage measurement amplifier upstream thereof, cannot be recognized or determined by the processor and thus cannot be compensated.